Devices for seeding, fertilizing and for applying chemicals such as herbicides, fungicides and pesticides in an agricultural field (which device or devices are hereinafter collectively referred to as a “seeder” or “seeders”) may include seeders such as the apparatus described in U.S. Pat. No. 7,159,523 B2 to Bourgault and Cresswell, which provides a frame which may be drawn by a tractor unit by way of a draw hitch, a trailing arm pivotally connected at the front end thereof to the frame, and a packer wheel rotatably attached to the rear end thereof, a furrow opener for creating a furrow attached to the trailing arm ahead of a seed boot (the seed boot being attached to a source of seed or chemical, through which seed boot the seed or other chemical may pass for insertion into the furrow created by the furrow opener), the packer wheel rolling along behind the furrow opener and seed boot, firmly packing the seeded furrow.
To ensure effective and consistent germination of the seeds planted in the furrows, and to securely position within the furrow any chemical product which has been applied during the seeding process, it is desirable to provide adequate, but not excessive, and adjustable downward force on the packing wheel. Furthermore, to ensure that the seeds and/or chemical products are inserted into the ground at a desirable and consistent depth in the ground, it is desirable to maintain the furrow opener at a constant and predetermined depth.